The present invention relates in general to magnetic transporation technology, and in particular to a new and useful method and device for accurately determining the distance from a reaction rail of a magnetic suspension railroad.
The invention concerns a method and a device for accurately determining the distance of a magnetic sensor from a conductive reaction rail, where the sensor has a measurement coil which has alternating voltage applied to it, and the coil current, which is dependent on the distance of the measurement coil from the reaction rail, is used to measure the distance. Particularly in magnetic bearings and magnetic suspension devices, as they are used for bearing regulation of support and guide magnets in magnetic transportation technology, the distance of the magnet must be continuously measured, in order to obtain a signal with which the magnet is controlled in such a way, with regard to the energizing current, that it remains suspended at the predetermined distance. Contact free measurement of a distance has already been studied in many ways.
According to a method known from German OS-28 03 877 the magnetic coupling of two coils, which is dependent on the distance, is utilized. But a disadvantage here is the great sensitivity with regard to the frequency which energizes the coils since the coils are operated in a resonance circuit with feed at a fixed frequency. Because of a low useful signal, this arrangement is sensitive to external electrical and magnetic interference fields.
The method described in German OS No. 32 37 843 uses ferromagnetic material to gude the magnetic flow within the sensor. This results in an influence of the sensor properties caused by external magnetic fields and a restriction to measurement of the distance relative to a ferromagnetic reaction rail.
The device described in German OS No. 29 16 289, to measure the air gap size, covers a large area of the grooved reaction rail and therefore has the disadvantage of large geometrical dimensions.
All of the known methods and devices have one thing in common, which is that no accurate monitoring of the sensor signal for distance takes place. This has the result that in case of an error within the sensor, the senso signal can take on a value which corresponds to a large distance of the sensor from the reaction rail, while in fact the distance is small.
Depending on the use and application of the sensor, this can result in restrictions or even in conditions that are critical for safety.
If the distance measurement is used in a magnetic suspension device, the error that although the mechanical distance is small, a signal corresponding to a large distance is given off, would lead to greater excitation of the magnet, in order to decrease the distance, thereby leading to contact between the magnet and the magnet reaction rail, with high magnetic pressure force. This represents a significant safety risk.